The present document is based on Japanese Priority Document JP 2001-207611, filed in the Japanese Patent Office on Jul. 9, 2001, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic disk having an embossed pattern for reproducing a servo position signal or ROM data.
2. Description of the Related Art
For magnetic disks, a servo position signal is written into every completed disk to realize precise head positioning for a higher track density. The writing of the servo position signal requires head feed while accurate positioning is performed with a pitch equal to a fraction of an intended track pitch. This needs a servo track writer provided with an extremely accurate positioning mechanism and a process taking a long processing time for writing. Thus, the above method requires higher accuracy and a longer processing time as the track density is higher, which causes an increase in manufacturing cost of the magnetic disks.
As a means for solving the aforementioned problem, a proposed magnetic disk with an embossed pattern has a servo pattern previously formed thereon as projections and depressions in a substrate. This type of disk requires magnetizing operation for obtaining a reproduced signal from the embossed pattern. The magnetizing operation, however, does not need positioning, and the accuracy of the servo pattern is determined by the accuracy of a matrix used in forming the embossing, so that a more accurate servo pattern can be formed readily and simply in a short time.
In this case, as an example of the aforementioned magnetic disk with an embossed pattern, proposed is a magnetic disk having a magnetic film on an upper surface of an embossed pattern and a magnetic film on a lower surface of the embossed pattern such that the magnetic films are magnetized in opposite directions as shown in FIG. 10 (JP Patent Number No. 2831078). Specifically, in the magnetic disk, two types of heads with different gap lengths are used, and the magnetic films on the upper and lower surfaces of the embossed pattern are first simultaneously magnetized in the same direction by the head with a larger gap length, and then only the magnetization of the magnetic film on the upper surface is reversed in the opposite direction by the head with a smaller gap length.
As described above, the magnetic disk in JP Patent Number No. 2831078 has the opposite directions of magnetization in the upper and lower surfaces of the embossed pattern. In this case, in the above magnetic disk, an inclined portion between the upper surface and the lower surface of the embossed pattern is in a demagnetized state or a magnetization transition area in which the direction of magnetization is unfixed.
According to studies of the present inventors, however, the magnetic disk in JP Patent Number No. 2831078 fails to form a favorable reproduced signal from the embossed pattern. For example, when the inclined portion is in a demagnetized state (without magnetization) as shown in FIG. 10, magnetization is present independently in the upper surface and the lower surface and no signal is produced from the inclined portion. Thus, a reproduced signal produced from magnetization caused in the lower surface involves spacing loss with respect to a reproduced signal produced from magnetization caused in the upper surface due to the distance in a depth direction of the embossed pattern, so that high quality cannot be expected in the resulting reproduced signal obtained by combining those signals.
The present invention has been made in view of the aforementioned circumstances, and it is desirable thereof to provide a magnetic disk with an embossed pattern capable of producing a favorable reproduced signal from the embossed pattern.
As a result of various studies for achieving the aforementioned aspect, the inventors of the present invention found that, in a magnetic disk with an embossed pattern, magnetization is given to a magnetic film in an inclined portion or a vertical portion between an upper surface and a lower surface of the embossed pattern such that the direction of the magnetization in cross section along the circumferential direction of the magnetic disk is parallel with the magnetic film, and a magnetization reversal area is formed in the magnetic film in the inclined portion or the vertical portion, thereby making it possible to form a favorable reproduced signal from the embossed pattern. In other words, the present inventors found that a favorable reproduce signal is not obtained simply from different directions of magnetization in the upper surface and the lower surface of the embossed pattern but the directions of magnetization and magnetization reversal in the inclined portion or the vertical portion of the embossed pattern contribute to output of a reproduced signal, and a favorable reproduced signal may be obtained by controlling the directions of magnetization and the magnetization reversal in the inclined portion or the vertical portion.
The present invention has been made on the basis of the aforementioned findings, and provides a magnetic disk with an embossed pattern having a magnetic film formed on a substrate provided with an erose embossed pattern on a surface along a circumferential direction, the embossed pattern having an upper surface, a lower surface, and a inclined portion or a vertical portion between the upper surface and the lower surface, wherein at least the magnetic film in the inclined portion or the vertical portion of the embossed pattern is magnetized, the direction of the magnetization in the magnetic film in the inclined portion or the vertical portion in cross section in the circumferential direction of the magnetic disk is substantially parallel with the film surface of the magnetic film, and the magnetic film in the inclined portion or the vertical portion has a magnetization reversal area.
In this manner, the magnetic disk with the embossed pattern according to the present invention can form a favorable reproduced signal from the embossed pattern.